Device and method for measuring the injection quantity of injection nozzles, especially for motor vehicles

ABSTRACT

A device ( 20 ) is used for measuring the injection quantity of injection nozzles ( 30 ). It includes a measuring chamber ( 22 ) to which the injection nozzle ( 30 ) can be coupled. In addition, a detection device is provided, which detects a state change of the testing fluid ( 60 ) in the measuring chamber ( 22 ) due to an injection by the injection nozzle ( 30 ). In order to be able to measure the injection quantity without wear and in a highly precise manner, the invention provides that the detection device has a capacitor, whose one electrode is comprised of an electrically conductive fluid ( 62 ), which is at least partially contained in a volume connected to the measuring chamber ( 22 ). The processing unit ( 58 ) is connected to the capacitor in such a way that it can detect a change in its capacitance, which is produced by a movement of the electrically conductive fluid ( 62 ).

PRIOR ART

[0001] The current invention relates firstly to a device for measuringthe injection quantity of injection nozzles, in particular for motorvehicles and in particular in production testing, which has at least onemeasuring chamber that is at least partially filled with a testingfluid, a coupling device that can couple at least one injection nozzleto the measuring chamber, a detection device, which detects a statechange of the testing fluid in the measuring chamber at leastintermittently during an injection by the injection nozzle, and aprocessing unit, which, based on the signal from the detection device,determines an injection quantity that corresponds to the state change.

[0002] A device of this kind is known on the market and is referred toas an injected fuel quantity indicator. This component is comprised of acylinder in which a piston is guided. The inner chamber of the cylinderand the piston define a measuring chamber. This measuring chamber has anopening against which an injection nozzle can be placed in apressure-tight manner. When the injection nozzle injects fuel into themeasuring chamber, the piston moves, which is detected by a travelsensor. The volume change of the measuring chamber and therefore theinjected fuel quantity can be calculated from the distance traveled bythe piston.

[0003] The known injected fuel quantity indicator, however, has variousdisadvantages. On the one hand, it has moving parts, which are subjectto wear with a continuous use of such a device. This wear is relativelysignificant because modern injection nozzles are tested not only inrandom spot checks but also continuously during production. In thecourse of the service life of such an injected fuel quantity indicator,this wear distorts the measuring results and ends up shortening theservice life of the injected fuel quantity indicator.

[0004] Moreover, friction is produced between the piston and thecylinder, which hinders the free movement of the piston and results inthe fact that the movement of the piston does not fully correspond tothe fuel volume actually injected. The measuring precision of theinjected fuel quantity indicator is therefore limited. Finally,particularly with injection nozzles for modern diesel engines, it isalso necessary to be able to reliably measure very small injectionquantities. Measurements of this kind are either difficult or completelyimpossible with the known injected fuel quantity indicator.

[0005] The object of the current invention, therefore, is to modify adevice of the type mentioned at the beginning so that it can measure theinjection quantity of injection nozzles with high precision over itsentire service life and can also reliably measure very small injectionquantities.

[0006] This object is attained by virtue of the fact that the detectiondevice has a capacitor, whose one electrode is comprised of anelectrically conductive fluid, which is at least partially contained ina volume connected to the measuring chamber, and the processing unit isconnected to the capacitor in such a way that it can detect a change inits capacitance, which is produced by a movement of the electricallyconductive fluid.

[0007] Advantages of the Invention

[0008] There is no mechanical piston in the device according to theinvention. Instead, the volume change of the measuring chamber occurringduring an injection moves in a volume of an electrically conductivefluid. Naturally, even a movement of this kind is encumbered byfriction, but this is several orders of magnitude smaller than that of amechanical piston. The detection and quantification of the movement ofthe fluid volume also takes place without friction or wear since thefluid volume constitutes an electrode of a capacitor. The capacitancechange produced by a movement of the electrode can be detected withextremely high precision without any drift over the service life of thedevice.

[0009] Advantageous modifications of the invention are disclosed in thedependent claims:

[0010] One modification is characterized in that at least one elongatedelectrical conductor is disposed in the volume so that it extends in itslongitudinal direction through a moving boundary surface of theelectrically conductive fluid; the electrical conductor is insulated inrelation to the outside by means of a dielectric and thus constitutes astationary electrode of the capacitor.

[0011] This device according to the invention therefore uses a tubularcapacitor to detect a volume change of the testing fluid. This tubularcapacitor is comprised of an elongated electrical conductor, whichconstitutes a radially inner first electrode of the capacitor. Aninsulation is provided around the outside of this inner electrode. Thesecond electrode of the tubular capacitor is constituted by theelectrically conductive fluid. The capacitance of the tubular capacitordepends on the size of the electrodes. If a longer region of theelectrical conductor is encompassed by the electrically conductivefluid, then the capacitance of the capacitor is greater than when only acomparatively small length of the electrical conductor is encompassed bythe electrically conductive fluid.

[0012] The volume in which the electrically conductive fluid iscontained, however, is connected to the measuring chamber and thetesting fluid contained therein. If the volume of the testing fluidchanges, this correspondingly displaces the electrically conductivefluid, which moves the boundary surface of the electrically conductivefluid that the electrical conductor passes through. Consequently thisalso changes the length of the electrical conductor that is encompassedby the electrically conductive fluid, which in turn produces a change inthe capacitance of the tubular capacitor. This change in the capacitanceis detected by the processing unit. The change in the capacitance of thetubular capacitor thus produced can be expressed formulaically by thefollowing relationship:

dC<pF>=0.0556×dL<mm>×ε/ln(D/d),

[0013] where:

[0014] dC=change in capacitance

[0015] dL=boundary surface movement

[0016] ε=permittivity

[0017] D=outer diameter of the dielectric

[0018] d=outer diameter of the electrical conductor.

[0019] This permits the total elimination of moving parts from thedevice according to the invention. Therefore no wear or friction of anykind occur in such a measuring device. Therefore even extremely smallinjection quantities can be detected by the device according to theinvention.

[0020] The invention also provides that between the injection nozzle andthe moving boundary surface, a flow tranquilizer is provided, which inparticular, has a porous body, preferably a sintered body. This preventsan injection impulse, which is directed from the injection nozzle intothe measuring chamber, from producing turbulence in the conductive fluidor a deformation of the boundary surface, which can distort themeasuring result. Therefore the presence of such a flow tranquilizerresults in an even more precise overall measurement result.

[0021] Another modification provides that the volume constituted by theelectrically conductive fluid is at least partially bounded by aprestressed wall, in particular by a pneumatic spring. A prestressedwall or pneumatic spring of this kind pressurizes the electricallyconductive fluid, as a result of which the testing fluid, which iscontained in the measuring chamber and is connected to the electricallyconductive fluid, is subjected to a corresponding pressure. However,when the injection nozzle executes an injection and the attendant volumeincrease of the testing fluid occurs, the prestressing of the wall orthe pneumatic spring provide a space into which the electricallyconductive fluid displaced by the testing fluid can escape.

[0022] It is particularly preferable if the pneumatic spring has adiaphragm, which is acted on by a gas on one side. Such an embodiment ofthe pneumatic spring makes it possible to maintain a relatively constantpressure in the electrically conductive fluid and in the testing fluid.Moreover, a pneumatic spring of this kind requires no maintenancewhatsoever and the pressure in the electrically conductive fluid can bearbitrarily adjusted by means of a corresponding adjustment of the gaspressure behind the diaphragm.

[0023] The invention also discloses how the signal intensity can beincreased in a simple manner when there is a change in the capacitance:the invention therefore provides that the device has a number ofstationary electrodes that are disposed essentially parallel to oneanother and connected in parallel. This produces a number ofparallel-connected capacitors, which share a common electrode (namelythe electrically conductive fluid) and which consequently all experiencea capacitance change during an injection. This increases the measuringprecision considerably, particularly with small injection quantities.

[0024] The stationary electrode can be arranged in a particularlyfavorable manner if the volume with the electrically conductive fluid isessentially circular in cross section. The stationary electrodes, e.g.the electrical conductors, should then be arranged as parallel aspossible to the longitudinal direction of the volume.

[0025] The invention also provides that at least a part of thestationary electrodes, in terms of the radial direction, is disposed inthe centroids of surface areas that are essentially the same size. Inthis case, the “fluid” electrodes of the individual capacitors are thesame size and corresponding capacitors have essentially the samecapacitance or sensitivity. This facilitates the measurement. If thestationary electrodes are distributed uniformly over the cross section,this also has the advantage that the form of the boundary surface, whichis not necessarily absolutely flat, e.g. due to turbulence, is averagedover the individual capacitors or electrical conductors. This eliminatesdistortions due to the irregularity of the boundary surface, which aregeometrically greater than the average distance of the individualelectrical conductors from one another.

[0026] Preferably, the stationary electrodes have a dielectric coatingon the outside, which preferably contains Teflon. With a coating of thiskind, the thickness of the dielectric can be kept to a minimum and, dueto its water-repelling properties, Teflon prevents the buildup ofconductive aqueous surface deposits, which could distort themeasurements.

[0027] A modification of the device according to the invention providesthat the testing fluid is oil and the electrically conductive fluid iswater, in particular saline water. The use of oil as the testing fluidprovides a particular good simulation of the viscosity and flowproperties of diesel fuel, whereas water, in particular saline water,has the conductivity required to produce a capacitor.

[0028] In another modification, the invention provides that the boundarysurface of the electrically conductive fluid directly adjoins thetesting fluid. A device embodied in this manner is primarily suitablewhen the testing fluid and electrically conductive fluid are comprisedof materials that do not mix. This includes, for example, theabove-mentioned material combination of oil and water.

[0029] Finally, in another modification, the invention provides that thedevice includes a housing, which at least partially contains the volumewith the electrically conductive fluid, and that the housing contains anelectrically conductive material, which is electrically connected to theprocessing unit, and the stationary electrode is insulated in relationto the housing. In this embodiment of the device according to theinvention, a simple connection is produced between the processing unitand the electrode comprised by electrically conductive fluid.

[0030] The invention also relates to a method for measuring theinjection quantity of injection nozzles, particularly for motor vehiclesand particularly in production testing, in which an injection nozzle iscoupled in a pressure-tight manner to a measuring chamber that is atleast partially filled with a testing fluid, the state change of thetesting fluid due to an injection of the injection nozzle into themeasuring chamber is detected, and an injection quantity is determinedbased on the state change.

[0031] In order to increase the measuring precision, the inventionprovides that a state change of the testing fluid results in a movementof an electrically conductive fluid, which in turn constitutes anelectrode of a capacitor, and the change in the capacitance of thecapacitor is detected, which is produced by a movement of the boundarysurface of the electrically conductive fluid. A method of this kindfunctions without any moving parts so that distortions of themeasurement due to friction and the wear associated with it can besignificantly reduced or even eliminated. The method according to theinvention therefore functions with very high precision.

[0032] DRAWINGS

[0033] An exemplary embodiment of the invention will be explained indetail below in conjunction with the accompanying drawings.

[0034]FIG. 1 shows a schematic, partially sectional side view of adevice for measuring the injection quantity of injection nozzles;

[0035]FIG. 2 shows a view of a detail of the device from FIG. 1; and

[0036]FIG. 3 shows a section through the device from FIG. 1, along theline III-III.

[0037] DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0038] In FIG. 1, a device for measuring the injection quantity ofinjection nozzles is labeled with the reference numeral 20. It includesa cylindrical measuring chamber 22, which is produced in the upperregion of a cylindrical housing 24. At the upper end of the housing 24in FIG. 1, there is an opening 26, which is externally encompassed by anO-ring seal 28. The tip of an injection nozzle 30 is placed against it.This injection nozzle 30 is one of the kind used in internal combustionengines for motor vehicles and in this instance, particularly forinternal combustion engines that operate with direct injection of dieselor gasoline. As a rule, the opening 26 is closed by a valve (not shown),which only opens when an injection nozzle 30 is placed onto the O-ringseal 28 or is inserted into the opening 26.

[0039] The housing 24 is comprised of metal. A total of 19 elongatedelectrical conductors pass through its bottom end and extend upward,parallel to the longitudinal axis of the housing 24, until slightlybeyond half the height of the housing 24. For the sake of clarity, onlyfive conductors are shown in FIG. 1, which are labeled with thereference numerals 5, 10, 15, 17, and 19. FIG. 3 shows all 19 of theconductors and they are labeled the reference numerals 1 to 19. As isclear from FIG. 3, the electrical conductors 1 to 19 are disposed in thecentroids of surface areas that are the same size. The reason for thiswill be explained later. As is clear from FIG. 2, the electricalconductors 1 to 19 are each covered with a dielectrical coating 32 onthe outside. The electrical conductors 1 to 19 are also electricallyinsulated in relation to the housing 24 and are connected to adistributing line 34 outside the housing 24. A disk-shaped sintered body36 is disposed in the measuring chamber 22, between the upper ends ofthe electrical conductors 1 to 19 in FIG. 1 and the opening 26 in thehousing 24.

[0040] A line 38 branches from the lower region of the housing 24 andleads to an equalizing vessel 40. On the whole, this equalizing vesselis ball-shaped and as a rule, a horizontal diaphragm 42 is stretchedacross its upper region. The space between the diaphragm 42 and theupper region of the equalizing vessel 40 is filled with a gas, thusproducing a pneumatic spring 44. The measuring chamber 22 in the upperregion of the housing 24 is also connected to an overflow 50 by means ofa line 46 and a valve 48. A line 52 also branches from the lower regionof the housing 24 and can be connected to a supply device 56 by means ofa valve 54. Finally, an electronic processing unit 58 is provided, whichis electrically connected to the distributing line 34 on the one handand is connected to the metallic housing 24 on the other.

[0041] As is particularly clear from FIG. 1, the measuring chamber 22 isfilled with a testing oil 60, which has a finite and knowncompressibility. The lower region of the housing 24 is filled with anelectrically conductive fluid, in the current instance, a saline watersolution 62. Since the testing oil 60 is specifically lighter than thesaline water solution 62, the stratification shown in FIG. 1 occursautomatically. The saline water solution 62 directly adjoins a boundarysurface 64 of the testing oil. The quantities of the testing oil 60disposed in the housing 24 and of the saline water solution 62 arematched to each other so that the boundary surface 64 lies somewhatbelow the upper ends of the electrical conductors 1 to 19.

[0042] The electrical conductors 1 to 19 and the saline water solution62 encompassing them constitute a total of 19 tubular capacitors, whoseone electrode is constituted by the electrical conductors 1 to 19 andwhose other electrode is constituted by the saline water solution 62.The two electrodes are separated from each other by the thickness of thedielectric coating 32. The capacitance of an individual capacitor thusproduced is calculated according to the following relationship:

C=0.0556×L×ε:ln(D/d),

[0043] where:

[0044] C=capacitance,

[0045] L=longitudinal span of an electrical conductor 1 to 19, which isencompassed by saline water solution 62,

[0046] ε=permittivity,

[0047] D=outer diameter of the dielectric coating 32,

[0048] d=outer diameter of an electrical conductor 1 to 19.

[0049] The fact that the capacitors, which are comprised of theelectrical conductors 1 to 19 and the saline water solution 62, areparallel connected by means of the distributing line 34 produces anoverall capacitance that corresponds to 19 times the individualcapacitance of one capacitor. The above relationship shows that thecapacitance C is a function of the longitudinal span of the electricalconductor 1 to 19, which is encompassed by saline water solution 62. Itshould be noted at this point that in the region of the electricalconductors 1 to 19, which is encompassed by testing oil 60, the outerelectrode is constituted by the metal housing 24. Comparativelyspeaking, this housing is spaced very far apart from the electricalconductors 1 to 19 so that its capacitance is negligibly low incomparison to the capacitance mentioned above.

[0050] If the longitudinal span of an electrical conductor 1 to 19,which is encompassed by saline water solution 62, changes due to thefact that the boundary surface 64 moves by an amount dL (see FIG. 2),then this also changes the capacitance of the corresponding capacitor.In the current device 20 for measuring the quantity of testing oil 60injected into the measuring chamber 22 by the injection nozzle 30, thisinterrelationship is used in the following manner:

[0051] When the injection nozzle 30 injects testing oil into the housing24 through the opening 26, the volume of the testing oil 60 in themeasuring chamber 22 increases due to the known and finitecompressibility of the testing oil 60. As a result, the saline watersolution 62 is displaced from the housing 24 by the amount of theinjected volume, which in turn means that the boundary surface 64 movesdownward by an amount dL. The saline water solution 62 thus flowsthrough the line 38 into the equalizing vessel 40 and presses thediaphragm 42 slightly upward, counter to the gas pressure of thepneumatic spring 44. Therefore the pneumatic spring 44 keeps the salinewater solution 62 and the testing oil 60 at an essentially constantpressure.

[0052] The movement of the boundary surface 64 by the amount dL changesthe capacitance of each respective capacitor, which are each constitutedby an electrical conductor 1 to 19 and the saline water solution 62, bythe value dC. This value is calculated according to the followingformula:

dC=0.0556×dL×ε/ln(D/d).

[0053] Since the individual capacitors are distributed uniformly overthe cross sectional area of the housing 24, irregularities in theboundary surface 64 caused by turbulences are averaged out andcompensated. However, turbulences in the vicinity of the boundarysurface 64 are already largely prevented by the sintered body 36. Thetotal capacitance change of all 19 capacitors therefore corresponds to19 times the capacitance change of a single capacitor. Such a change inthe capacitance of the capacitors is detected by the processing unit 58and converted into an injection volume according to a previously storedcalibration table.

[0054] The device 20 described above can consequently detect thequantity of a testing oil 60 injected into the measuring chamber 22 bythe injection nozzle 30, without the need for moving mechanical parts inthe device 20. Moreover, the possibility of placing a large number ofindividual capacitors in the housing 24, permits an “amplification” ofthe signal so that even extremely small injection quantities can bereliably detected. The precision of the measurement is also increased bythe sintered body 36, which serves to keep turbulences produced in themeasuring chamber 22 by the spray of the injection nozzle 30 away fromthe capacitors constituted by the electrical conductors 1 to 19 and thesaline water solution 62. Because the individual capacitors are disposedin the centroids of surface areas that are the same size, theircapacitances can be simply added up without requiring a weighting of theindividual capacitors in relation to other capacitors.

[0055] The device 20 can be used just as easily on theinlet/high-pressure side of an injection nozzle 30 as on theoutlet/low-pressure side. It can be used for virtually any pressures.The maximal possible pressure is in principle limited only bysafety-related aspects of the components used for the device 20. Throughthe selection of suitable geometric dimensions and a suitable number ofcapacitors, the device 20 can be adapted to any measuring requirement.

1. A device for measuring the injection quantity of injection nozzles(30), in particular for motor vehicles and in particular in productiontesting, which has at least one measuring chamber (22) that is at leastpartially filled with a testing fluid (60), a coupling device (28) thatcan couple at least one injection nozzle (30) to the measuring chamber(22) in a pressure-tight manner, a detection device, which detects astate change of the testing fluid (60) in the measuring chamber (22) atleast intermittently during an injection by the injection nozzle (30),and a processing unit (58), which, based on the signal from thedetection device, determines an injection quantity that corresponds tothe state change, characterized in that the detection device has acapacitor, whose one electrode is comprised of an electricallyconductive fluid (62), which is at least partially contained in a volumeconnected to the measuring chamber (22), and the processing unit (58) isconnected to the capacitor in such a way that it can detect a change inits capacitance, which is produced by a movement of the electricallyconductive fluid (62).
 2. The device according to claim 1, characterizedin that at least one elongated electrical conductor (1 to 19) isdisposed in the volume so that it extends in its longitudinal directionthrough a moving boundary surface (64) of the electrically conductivefluid (62); the electrical conductor (1 to 19) is insulated in relationto the outside by means of a dielectric (32) and thus constitutes astationary electrode of the capacitor.
 3. The device according to one ofclaims 1 or 2, characterized in that between the injection nozzle andthe moving boundary surface (64), a flow tranquilizer is provided, whichin particular, has a porous body, preferably a sintered body.
 4. Thedevice according to one of the preceding claims, characterized in thatthe volume constituted by the electrically conductive fluid (62) is atleast partially bounded by a prestressed wall (42), in particular by apneumatic spring (44).
 5. The device according to claim 4, characterizedin that the pneumatic spring (44) has a diaphragm (42), which is actedon by a gas on one side.
 6. The device according to one of the precedingclaims, characterized in that it has a number of stationary electrodes(1 to 19) that are disposed essentially parallel to one another andconnected in parallel.
 7. The device according to one of the precedingclaims, characterized in that the volume is essentially circular incross section.
 8. The device according to claim 7, characterized in thatat least a part of the stationary electrodes (1 to 19), in terms of theradial direction, is disposed in the centroids of surface areas that areessentially the same size.
 9. The device according to one of thepreceding claims, characterized in that the stationary electrodes (1 to19) have a dielectric coating (32) on the outside, which preferablycontains Teflon.
 10. The device according to one of the precedingclaims, characterized in that the testing fluid is oil (60) and theelectrically conductive fluid is water, in particular saline water (62).11. The device according to one of the preceding claims, characterizedin that the boundary surface (64) of the electrically conductive fluid(62) directly adjoins the testing fluid (60).
 12. The device accordingto one of the preceding claims, characterized in that it includes ahousing (24), which at least partially contains the volume with theelectrically conductive fluid (62), and that the housing (24) containsan electrically conductive material, which is electrically connected tothe processing unit (58), and the stationary electrode (1 to 19) isinsulated in relation to the housing.
 13. A method for measuring theinjection quantity of injection nozzles (30), particularly for motorvehicles and particularly in production testing, in which at least oneinjection nozzle (30) is coupled in a pressure-tight manner to ameasuring chamber (22) that is at least partially filled with a testingfluid (60), the state change of the testing fluid (60) due to aninjection of the injection nozzle (30) into the measuring chamber (22)is detected, and injection quantity is determined based on the statechange, characterized in that a state change of the testing fluid (60)results in a movement of an electrically conductive fluid (62), which inturn constitutes an electrode of a capacitor, and the change in thecapacitance of the capacitor is detected, which is produced by amovement of the boundary surface (64) of the electrically conductivefluid (62).